First, the empty topic is in general a discourse rather than a sentence phenomenon.

The reviewer is perforce required to deal with major themes and how topics within them are treated.

Origin

Late 15th century (originally denoting a set or book of general rules or ideas): from Latintopica, from Greekta topika, literally 'matters concerning commonplaces' (the title of a treatise by Aristotle), from topos 'a place'.

This was originally written common place, a translation of Latin locus communis, rendering Greek koinos topos ‘general theme’, terms for a passage on which a speaker could base an argument. In the past people would keep commonplace books of such passages, and the quoting of these no doubt led to the modern sense of the word. Topic (Late Middle English) was originally a word for a set or book of general rules or ideas. It comes from Latin topica, from Greek ta topika, meaning literally ‘matters concerning commonplaces’ (the title of a treatise by Aristotle). Early use was as a term in logic and rhetoric describing a rule or argument as ‘applicable in most but not all cases’. See also utopia. Common itself (Middle English) comes via French from Latin communis ‘common, general’ also the source of commune (late 17th century), communism (mid 19th century), communication, communion, and community [all LME].